Understanding how the "audience" concept actually works

I am trying my best to fully understand the relationship between Applications, APIs, Audience, and Scopes within the world of Auth0 and oauth 2.0. I think the best way to illustrate the relationships is through an example. Let’s say I have a service topology for the following system 1 Application to many APIs www.foo.com is the Application that services a SPA and is backed by 2 APIs, bar.foo.com a